"Scott Dorsey" wrote in message
...
Henry Kolesnik wrote:
The secondary of the IF xfmrm feeding the diode will have
a different
winding than the first two. My transformer theory is not
up to snuff,
I'm 68 and if I recall correctly a diode has a much lower
input
impedance that has to be matched so I'm guessing it will
have less
turns. Remember that a transformer reflects the impedance
back.
You may want to get a copy of The Radiotron Designers
Handbook by
Langford, it covers just about anything you would want to
know about
tube radios, over 1000 pages.

The over 1000-page one is the Fourth Edition, which is the
most expensive
on the used market, and the one which has the most hi-fi
information in
it.

The discussion of IF strip design is also in the smaller
and much less
expensive Third Edition. Some people like the third
edition because it
has some information on transformer design which was not
carried into
the fourth.

A copy of the fourth edition is available online he
http://geek.scorpiorising.ca/RDH4.html
--scott
The forth edition is available in PDF form from Pete
Milette's site:
http://www.pmillett.com/
Along with many other classic books including
K.R.Sturley's two volume book on radio receiver design. The
organization of the site is a bit confusing so a bit of
poking around in needed to find everything. The quality of
his scans is excellent but the files are _very_ large and
really require a high speed connection to be practical.
I also recommend the 4th edition of the Radiotron, I
think I have two, the one I bought new fell apart from use
(rebound it). The 3rd edition, which is much smaller, also
has a lot of useful information in it.
I agree with the statements made about the final IF
transformer but not all detectors offer low impedance to the
transformer although this is true of straight diode
detectors. Both of the above books have thorough discussions
of AM detectors and their relative merits.

--
Richard Knoppow
Los Angeles
WB6KBL

The particular receiver Theo was asking about uses a 6SQ7 dual-diode, triode
as a diode detector. I found it in the 1950 Radio Amateur's Handbook.

The schematic may be a bit misleading, though, since it shows a schematic of
the diode transformer that is the same as an if transformer - which is tuned
primary and tuned secondary - with the full winding on the secondary used
for the diode. I found this concise statement in the 1942 Editors and
Engineers Radio Handbook "Diodes load the tuned circuit to which they are
connected, however, and thus reduce selectivity slightly. Special i.f.
transformers are used for the purpose of providing a low-impedance input
circuit to the diode detector."

If I were winding the i.f. transformer, I would use a hi-q secondary and tap
down for the diode, so that selectivity is maintained, while properly
matching the diode input impedance. That may be how the transformer is
connected, although it does not show that on the schematic.

Colin K7FM

Colin
I'm curious as to how you know what Rx Theo was asking about since I've
not seen it mentioned?

--
Thanks & 73
Hank WD5JFR
"COLIN LAMB" wrote in message
m...
The particular receiver Theo was asking about uses a 6SQ7 dual-diode,
triode as a diode detector. I found it in the 1950 Radio Amateur's
Handbook.

The schematic may be a bit misleading, though, since it shows a
schematic of the diode transformer that is the same as an if
transformer - which is tuned primary and tuned secondary - with the
full winding on the secondary used for the diode. I found this
concise statement in the 1942 Editors and Engineers Radio Handbook
"Diodes load the tuned circuit to which they are connected, however,
and thus reduce selectivity slightly. Special i.f. transformers are
used for the purpose of providing a low-impedance input circuit to the
diode detector."

If I were winding the i.f. transformer, I would use a hi-q secondary
and tap down for the diode, so that selectivity is maintained, while
properly matching the diode input impedance. That may be how the
transformer is connected, although it does not show that on the
schematic.

Colin K7FM

I cheated by asking him.

Colin K7FM

Colin
The diode load resistor in most of the diode detector circuits I'm
familiar with have several hundred kilo ohms and I think 6SQ7 diode has
a few hundred ohms so the total reflected impedance to the last IF is
the pretty much the resistive load. And if my 68 yr old memory serves
me right most commonly used IF transformers had an input and output part
number and in some cases interstage but that may have been for TV IF. I
don't recall replacing many transformers because they failed
electrically but because the little ferrite core with a hex hole would
crack and could no longer be turned. Many times this was because of a
previous repair where a monkey not a tech, tried to tweak it and broke
the core.
I also worked on a one set that had the first IF transformer installed
backwards at the IF mfg factory, not the TV assembly plant. That took
some time to find considering the test eqpt at hand was limited to a
vtvm and an audio scope.
Time to stop rambling and ask if the ARRL article distinguished the IF
transformers with different part numbers?

--
Thanks & 73
Hank WD5JFR
"COLIN LAMB" wrote in message
m...
The particular receiver Theo was asking about uses a 6SQ7 dual-diode,
triode as a diode detector. I found it in the 1950 Radio Amateur's
Handbook.

The schematic may be a bit misleading, though, since it shows a
schematic of the diode transformer that is the same as an if
transformer - which is tuned primary and tuned secondary - with the
full winding on the secondary used for the diode. I found this
concise statement in the 1942 Editors and Engineers Radio Handbook
"Diodes load the tuned circuit to which they are connected, however,
and thus reduce selectivity slightly. Special i.f. transformers are
used for the purpose of providing a low-impedance input circuit to the
diode detector."

If I were winding the i.f. transformer, I would use a hi-q secondary
and tap down for the diode, so that selectivity is maintained, while
properly matching the diode input impedance. That may be how the
transformer is connected, although it does not show that on the
schematic.

Colin K7FM

"Time to stop rambling and ask if the ARRL article distinguished the IF
transformers with different part numbers?"

Yes

The first and second stage transformers are designated "456 kc interstage if
transformer, permeability-tuned (Millen 64456)". The third if transformer
(to the diode detector) is designated "456 kc diode transformer,
permeability-tuned (Millen 65454)".

The schematic drawing for all three transformers are the same, but the
secondary of the last transformer would be different to attain a lower
impedance.

73, Colin K7FM

Colin
Good on yah mate..
Now to express it another way the winding ratio of the diode transformer
has to be such that when it reflects the diode and its load to the plate
of the last IF, the plate circuit will see the correct impedance for the
IF tube load. Transformers don't have impedance, only turns ratio to
reflect back whatever impedance they see in accordance with the turns
ratio.

--
73
Hank WD5JFR
"COLIN LAMB" wrote in message
m...
"Time to stop rambling and ask if the ARRL article distinguished the
IF transformers with different part numbers?"

Yes

The first and second stage transformers are designated "456 kc
interstage if transformer, permeability-tuned (Millen 64456)". The
third if transformer (to the diode detector) is designated "456 kc
diode transformer, permeability-tuned (Millen 65454)".

The schematic drawing for all three transformers are the same, but the
secondary of the last transformer would be different to attain a lower
impedance.

73, Colin K7FM

"Henry Kolesnik" wrote in message
...
Colin
Good on yah mate..
Now to express it another way the winding ratio of the diode transformer
has to be such that when it reflects the diode and its load to the plate
of the last IF, the plate circuit will see the correct impedance for the
IF tube load. Transformers don't have impedance, only turns ratio to
reflect back whatever impedance they see in accordance with the turns
ratio.

Thats fine for untuned transformers, but surely in the case of these I.F.
transformers that consist of mutually coupled parallel tuned circuits, this
must be different?

A tuned circuit is a reactive load just like an untuned circuit except
its reactance is max at the desired frequency. Any DC resistance such
as the diode and it's load are undesirable as they lower Q.

--
73
Hank WD5JFR
"Theo" wrote in message
...

"Henry Kolesnik" wrote in message
...
Colin
Good on yah mate..
Now to express it another way the winding ratio of the diode
transformer has to be such that when it reflects the diode and its
load to the plate of the last IF, the plate circuit will see the
correct impedance for the IF tube load. Transformers don't have
impedance, only turns ratio to reflect back whatever impedance they
see in accordance with the turns ratio.

Thats fine for untuned transformers, but surely in the case of these
I.F. transformers that consist of mutually coupled parallel tuned
circuits, this must be different?